For many years, metal parts have been joined using silver-based brazing compounds. As is well known in the art, it is necessary to prepare the surfaces to be joined prior to applying the brazing compounds in order to provide adhesion of the brazing compound to the surfaces to be joined. This preparation is typically performed by a flux material, which is applied to the joint and activated by the application of heat to the joint. Once activated, the flux thoroughly cleans the surfaces to the joined and removes any oxides that will degrade the strength of the brazed joint.
As they must aggressively clean the surfaces to be joined, fluxes have typically been highly corrosive and hygroscopic in nature. Accordingly, it is necessary in many applications to remove any residual flux or flux residue from the joined parts in order to prevent corrosion of the parts. This removal increases the overall costs of the parts, due to the additional process steps and the cost of waste disposal from the cleaning process. In addition, the waste generated by this cleaning is hazardous to humans and harmful to the environment.
Finally, because of their corrosiveness and affinity for absorbing water, many typical fluxes have not been adapted for use in flux cored wires. As this is the case, the use of these fluxes has necessitated the additional step of applying the flux in a paste form prior to heating and joining the parts. As was the case with the cleaning step described above, the need to perform this additional step increases the overall cost of the joined parts.
Accordingly, there is a need for a flux for use with silver brazing compositions that effectively prepares the surfaces to be joined, is non-corrosive and non-hygroscopic and, accordingly, does not need to be cleaned from joined surfaces after they are joined, and may be formed into a powder for disposal within a flux cored wire.